-LRB- CNN -RRB- -- With extreme heat and the worst drought in half a century continuing to plague the farm states , there are important lessons to be learned for all of us -- farmers , consumers and the world 's poorest populations alike -- about the effect of climate change .

The Agriculture Department announced this season 's first major crop yield forecasts , and they were n't pretty : a nationwide average of 123.4 bushels of corn per acre , the lowest level since 1995 . Soybean yield is expected to be low too , though not as bad as corn .

The United States , which is the world 's largest producer and exporter of staple grains , is grappling with the biggest surprise in production shortfalls since the Dust Bowl of the 1930s . Certainly , this July surpassed July 1936 as the hottest month on record .

So , how will the devastation affect U.S. crop farmers ?

Drought , heat bring spiders out

Since mid-June , corn prices have risen about 60 % , more than twice the projected decline in yield . This means that farm revenue will go up . About 90 % of the corn acreage is backed by a generously subsidized federal insurance program , described by Steven Colbert as `` Obamacare for the corn , '' so crop farmers will be just fine . Livestock farmers who use corn to feed their animals could see higher costs , but most have contracts with processors who provide their feed grains .

What about consumers ? Will high commodity prices affect the prices of food you eat ? Not much , actually .

Commodity prices account for just a tiny share of retail food prices . If you 're a shrewd shopper , next year you may notice higher prices for meat , milk , eggs , and cheese and all types of processed foods . The USDA estimates that food prices will increase 3 to 4 % in 2013 . This is not going to radically change your life . People in rich countries like the U.S. are not going to eat much less or much differently as a result of modestly higher prices .

The crop losses will have the most effect on the world 's poorest populations . About 2 billion people still live on $ 2 a day or less . Many of them live in urban areas of developing countries . Often , they must spend half or more of their income on food , the bulk coming from staple grains like corn , wheat and rice . For these people , a huge rise in grain prices is more than noticeable -- it can literally break their budget .

In 2008 and 2011 , when corn prices went up to levels nearly as high as today 's , the world saw a sharp rise in food riots . Many pointed to wheat prices as a catalyst for revolutions in the Middle East , including Egypt , Tunisia and Libya . It is not hard to see that food-related security problems overseas could cost us far more than the extra pennies we 'll pay at the grocery store .

NASA scientist links climate change , extreme weather

The U.S. can ease price pains somewhat by suspending government rules that mandate biofuel production . In 2011 , about 40 % of U.S. corn crops were diverted to ethanol -LRB- a quarter , if we take into account that nutritional content is recycled back into feeds for animals in the form of distiller grains -RRB- . But this seems untenable politically .

The larger and more important issue is whether this year 's bad crop yield is an omen of what we should expect going forward .

Record high temperatures are occurring with far greater frequency than in decades past , and crop yields decline sharply in extreme heat . In research that Wolfram Schlenker and I have conducted using the Hadley III climate model , we project yield declines of about 20 % over the next 20 years , holding all else the same . This summer 's extreme heat may just become typical in 15 years .

Some have criticized these projections as too pessimistic , and they just might be . An atmosphere richer in carbon dioxide concentrations may allow plants to transpire less water during photosynthesis , and thus , improve drought tolerance . Farmers can adjust to earlier planting times , perhaps avoiding some extreme temperatures during the sensitive flowering period , and lengthening the growing season . And new drought-tolerant crop varieties have been developed .

This season was a good test of these adaptive strategies . It appears they did n't work . Carbon dioxide concentrations are much higher than they were in 1983 and 1988 , when it was nearly as hot as this summer . And farmers planted much earlier than usual , many using new drought-tolerant varieties .

Record drought is good business for some

For now , we can take a little comfort that ample harvests in the Dakotas , Minnesota and parts of the South could make up for some of the decimated crops in the central Midwest this year .

But next year ? And the years after ? In the long term , a warming world will be a difficult challenge for our crops and all of us .

Complete coverage : drought

The opinions expressed in this commentary are solely those of Michael Roberts .

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Michael Roberts : Extreme heat and drought are signs of a changing climate

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Roberts : Farmers and U.S. consumers will be fine ; food prices will go up a bit in 2013

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He says the crop losses will have the most effect on the world 's poorest populations

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Roberts : This summer 's extreme heat may just become typical in 15 years